New Class Of Antibacterial Agents Research Articles

Rational design of berberine-based FtsZ inhibitors with broad-spectrum antibacterial activity.

Inhibition of the functional activity of Filamenting temperature-sensitive mutant Z (FtsZ) protein, an essential and highly conserved bacterial cytokinesis protein, is a promising approach for the development of a new class of antibacterial agents. Berberine, a benzylisoquinoline alkaloid widely used in traditional Chinese and native American medicines for its antimicrobial properties, has been recently reported to inhibit FtsZ. Using a combination of in silico structure-based design and in vitro biological assays, 9-phenoxyalkyl berberine derivatives were identified as potent FtsZ inhibitors. Compared to the parent compound berberine, the derivatives showed a significant enhancement of antibacterial activity against clinically relevant bacteria, and an improved potency against the GTPase activity and polymerization of FtsZ. The most potent compound 2 strongly inhibited the proliferation of Gram-positive bacteria, including methicillin-resistant S. aureus and vancomycin-resistant E. faecium, with MIC values between 2 and 4 µg/mL, and was active against the Gram-negative E. coli and K. pneumoniae, with MIC values of 32 and 64 µg/mL respectively. The compound perturbed the formation of cytokinetic Z-ring in E. coli. Also, the compound interfered with in vitro polymerization of S. aureus FtsZ. Taken together, the chemical modification of berberine with 9-phenoxyalkyl substituent groups greatly improved the antibacterial activity via targeting FtsZ.

Restriction of the conformational dynamics of the cyclic acyldepsipeptide antibiotics improves their antibacterial activity.

The cyclic acyldepsipeptide (ADEP) antibiotics are a new class of antibacterial agents that kill bacteria via a mechanism that is distinct from all clinically used drugs. These molecules bind and dysregulate the activity of the ClpP peptidase. The potential of these antibiotics as antibacterial drugs has been enhanced by the elimination of pharmacological liabilities through medicinal chemistry efforts. Here, we demonstrate that the ADEP conformation observed in the ADEP–ClpP crystal structure is fortified by transannular hydrogen bonding and can be further stabilized by judicious replacement of constituent amino acids within the peptidolactone core structure with more conformationally constrained counterparts. Evidence supporting constraint of the molecule into the bioactive conformer was obtained by measurements of deuterium-exchange kinetics of hydrogens that were proposed to be engaged in transannular hydrogen bonds. We show that the rigidified ADEP analogs bind and activate ClpP at lower concentrations in vitro. Remarkably, these compounds have up to 1200-fold enhanced antibacterial activity when compared to those with the peptidolactone core structure common to two ADEP natural products. This study compellingly demonstrates how rational modulation of conformational dynamics may be used to improve the bioactivities of natural products.

Study on variability assessment and evolutionary relationships of glutamate racemase in Pseudomonas species

Pseudomonas species is known to cause multiple nosocomial infections in patients and results in high morbidity and mortality rates (10%). The greatest obstacle in treating patients infected with the Pseudomonas species is the widespread emergence of antibiotic resistance. Hence, there is an urgent need to develop new compounds which can be effective against Pseudomonas species and possibly remain tolerant to drug resistance. The enzyme glutamate racemase plays an important role in cell wall synthesis of bacteria and as a rate limiting step, thus it is an excellent target for the designing of new class of antibacterial agents. The objective of this study is to investigate the variations in sequences of glutamate racemase, a potential drug target across the all 31 species of Pseudomonas. Sequence variability and conservation for functional motif identification is helpful for identifying evolutionarily important residues with functional significance; subsequently these results of variable sites were supported by entropy profile obtained from protein variability server using Shannon entropy. Phylogenetic profile among the different Pseudomonas sp. having fully/highly conserved residues was observed, suggesting possible functional similarities between them. The variation analysis in conserved and non-conserved region of the sequence can be used to predict the binding site for target specific drug discovery.

Cyclic lipodepsipeptides: a new class of antibacterial agents in the battle against resistant bacteria.

In order to provide effective treatment options for infections caused by multidrug-resistant bacteria, innovative antibiotics are necessary, preferably with novel modes of action and/or belonging to novel classes of drugs. Naturally occurring cyclic lipodepsipeptides, which contain one or more ester bonds along with the amide bonds, have emerged as promising candidates for the development of new antibiotics. Some of these natural products are either already marketed or in advanced stages of clinical development. However, despite the progress in the development of new antibacterial agents, it is inevitable that resistant strains of bacteria will emerge in response to the widespread use of a particular antibiotic and limit its lifetime. Therefore, development of new antibiotics remains our most efficient way to counteract bacterial resistance.

Study of physical properties and biological activity of copper nanoparticles

Metals in the form of nanoparticles are one of the long-term challenges for the creation of a new class of antibacterial agents. The biological activity of nanoparticles of metals depends directly on their physical and chemical properties. The objective of this work is to study the physicochemical parameters and antibacterial effects of copper nanoparticles for the standardization of the given nanomaterial during further use as an antibacterial agent. The physical and chemical parameters and antibacterial effects of copper nanoparticles are investigated. Optical methods, including atomic force microscopy, spectrophotometry, and fluorometry, are used to determine the sizes of associates of nanoparticles. The size of copper nanoparticles was 75 nm, and the sizes of nanoparticle associates are 481.1–1037 nm. An oxide film without any admixture of organic molecules is detected on the surface of nanoparticles. The antibacterial effects of copper nanoparticles are studied on the basis of clinical polyantibiotic-resistant strains of epidermal staphylococcus and gramnegative nonfermentative microorganisms (causative agents of purulent flammatory diseases among patients of traumatology and orthopedic in-patient hospital departments). As a result of the investigations, a clear antibacterial effect of copper nanoparticles with specified physical characteristics on gram-positive and gram-negative microorganisms of causative agents of wound infection is detected, which gives prospects for the further use of these particles as antibacterial agents.

Staphylococcus aureus Formyl-Methionyl Transferase Mutants Demonstrate Reduced Virulence Factor Production and Pathogenicity

Inhibitors of peptide deformylase (PDF) represent a new class of antibacterial agents with a novel mechanism of action. Mutations that inactivate formyl methionyl transferase (FMT), the enzyme that formylates initiator methionyl-tRNA, lead to an alternative initiation of protein synthesis that does not require deformylation and are the predominant cause of resistance to PDF inhibitors in Staphylococcus aureus. Here, we report that loss-of-function mutations in FMT impart pleiotropic effects that include a reduced growth rate, a nonhemolytic phenotype, and a drastic reduction in production of multiple extracellular proteins, including key virulence factors, such as α-hemolysin and Panton-Valentine leukocidin (PVL), that have been associated with S. aureus pathogenicity. Consequently, S. aureus FMT mutants are greatly attenuated in neutropenic and nonneutropenic murine pyelonephritis infection models and show very high survival rates compared with wild-type S. aureus. These newly discovered effects on extracellular virulence factor production demonstrate that FMT-null mutants have a more severe fitness cost than previously anticipated, leading to a substantial loss of pathogenicity and a restricted ability to produce an invasive infection.

A Novel 8-Carbon Keto Saccharide Backbone from Roman Chamomile (Chamaemelum nobile L.)

Chamaemelum nobile (L.) Allioni, (syn. Anthemis nobilis L. or Chamomilla nobilis G.) is a perennial herb of the Asteraceae family, with the common name Roman chamomile. The plant has been widely used as household medicine for the treatment of a variety of health conditions [1]. The flowering tops of the plant are used to make teas, liquid extracts, capsules, or tablets sold as dietary supplements. A phytochemical investigation to explore the unknown constituents in the flowers of C. nobile led us to isolate and identify an 8-carbon keto saccharide acid and six of its derivatives. The structure of this 8-carbon sugar backbone was elucidated as β-3-deoxy-L-manno-2-octulopyranosonic acid, and its absolute structural configuration was completely assigned using 1D and 2D NMR techniques. This 8-carbon L-sugar skeleton has never been reported or isolated from a natural source. More interestingly, its D-isomer, namely 2-keto-3-deoxy-D-manno-octulosonic acid (KDO), is an essential component of the outer-cell membrane lipopolysaccharide (LPS) of gram-negative bacteria and plays critical roles in the biological system [2]. Inhibitors of KDO biosynthesis have the potential to be a new class of antibacterial agents [3].

Potential Pitfalls of Using Epichlorohydrin as Starting Material for Oxazolidinone Antibacterials

The importance of oxazolidinone functional group has been well documented in synthetic and medicinal chemistry. In the latter area, recent interests are focused on N-arylsubstituted oxazolidin-2-one structures, as exemplified by linezolid and eperezolid, which represent a new class of antibacterials with activity against drug-resistant Grampositive pathogens, including MRSA. Biologically active enantiomers of the oxazolidinone antibacterials are those with the (S)-configuration. Synthesis of the (S)-enantiomers have been achieved in enantiopure form starting from various glycidol derivatives such as (R)-glycidyl butyrate, (S)and (R)-epichlorohydrin, N-Boc-glycidylamine, and more recently, (R)-glycidyl tosylate. Other enantiopure starting materials include 3-chloro-1,2-propanediol, mannitol, protected glyceraldehyde, and aziridine-2carboxamide. Several routes employing asymmetric reactions have also been reported. Of those enantiopure starting materials, epichlorohydrin and glycidyl tosylate are particularly useful as they are doubly activated (at both C-1 and C-3) toward nucleophilic substitutions. The tandem, three-step sequence of the epoxide ring-opening, carbamate formation and oxazolidin-2one ring-closure (sometimes referred to as “1,3-cycloaddition”) represents an atom-economic key step in the synthesis of oxazolidinone antibacterials (Scheme 1). Yu et al. first employed this process with epichlorohydrin as the starting material; we then followed it up with glycidyl tosylate, and showed that this crystalline and storage-stable compound was a viable starting material for oxazolidinone antibacterials. Our work with glycidyl tosylate reminded us how the issues of regioand stereochemistry were entwined together for the doubly activated glycidol derivatives. It also prompted us to wonder how these issues had played out in Yu’s work with epichlorohydrin. As the details were not discussed in their original communication, we decided to reexamine the tandem, three-step sequence with epichlorohydrin as the starting material. The 1,3-cycloaddition reaction of (R)-epichlorohydrin and phenyl isocyanate was performed with a catalytic amount of LiBr. In the absence of detailed experimental procedure in the original work, also to make a meaningful comparison with our findings with glycidyl tosylate, we maintained the reaction conditions as close as possible to the ones employed in the glycidyl tosylate process [in THF (0.067 M) at reflux with phenyl isocyanate (3 eq) and LiBr (0.1 eq)]. Epichlorohydrin underwent the tandem, three-step sequence more slowly with LiBr than glycidyl tosylate did with LiI. The reaction took 8 h to complete (vs ~30 min for glycidyl tosylate/LiI). The desired chloro oxazolidinone product was isolated in 93% yield, seemingly validating the results in the original report. A careful examination, however, revealed the presence of a by-product, suggesting concurrent sidereaction pathway(s) and potential complications in the process. In order to gain a fuller picture of the process, we postulated possible reaction pathways for the 1,3-cycloaddition reaction of epichlorohydrin/PhNCO/LiBr and set out to assess the significance of each pathway quantitatively (Scheme 2). Model reactions revealed that the products could undergo secondary displacements, not one-way, but in both ways, hence Paths IV and V in addition to Path III. This raised an extra issue for the epichlorohydrin process. In the glycidyl tosylate process, a single reaction pathway was responsible for the formation of the desired product, whose stereochemical integrity was therefore maintained through the entire course of the reaction. In the epichlorohydrin process, on the other hand, we now needed to consider multiple pathways for the formations of the desired as well as undesired products (Paths I, IV and V for 2; Paths II and III for 3), each resulting in a distinct stereochemical outcome. Significance of these pathways may be assessed in a time study in which the enantiomeric purities as well as the chemical yields of both products would be determined at various reaction times.

ChemInform Abstract: Armeniaspiroles, a New Class of Antibacterials: Antibacterial Activities and Total Synthesis of 5‐Chloro‐Armeniaspirole A.

AbstractArmeniaspiroles, isolated from S.armeniacus, are characterized by a novel spiro[4.4]non‐8‐ene scaffold.

S-Guanylation of Human Serum Albumin is a Unique Posttranslational Modification and Results in a Novel Class of Antibacterial Agents

8-Nitroguanosine 3',5'-cyclic monophosphate (8-nitro-cGMP) is a nitric oxide metabolite and an important second messenger. 8-Nitro-cGMP reacts with sulfhydryl groups forming a novel posttranslational modification, namely, S-guanylation. In this work, we found, by using a quantitative competition enzyme-linked immunosorbent assay procedure, that S-guanylated human serum albumin (S-cGMP-HSA) is a component of normal plasma, and that hemodialysis patients decrease its concentration, on an average, from 68 to 34 nM. End-stage renal disease is often accompanied by septicemia, and we found that S-cGMP-HSA possesses an in vitro antibacterial effect with half maximal inhibitory concentration of approximately 2 μM against Escherichia coli American Type Culture Collection. Our findings indicate that S-cGMP-HSA can be regarded as an endogenous antibacterial agent in healthy conditions and as a useful new class of antibacterial agents with a circulation time sufficient for in vivo biological activity. The clinical development of S-cGMP-HSA as a safe and strong antibacterial agent arisen from endogenous posttranslational modification would be expected.

Armeniaspiroles, a new class of antibacterials: antibacterial activities and total synthesis of 5-chloro-Armeniaspirole A

Armeniaspiroles, a novel class of natural products isolated from Streptomyces armeniacus, are characterized by a novel spiro[4.4]non-8-ene scaffold. Various derivatives of Armeniaspiroles could be obtained by halogenation, alkylation, addition/elimination or reductions. A total synthesis of the 5-chloro analog of Armeniaspirole A has been accomplished in a linear six-step sequence. 5-Chloro-Armeniaspirole A exhibits good activity against a range of multidrug-resistant, Gram-positive bacterial pathogens.

Design, synthesis and evaluation of triazole functionalized ring-fused 2-pyridones as antibacterial agents

Antibacterial resistance is today a worldwide problem and the demand for new classes of antibacterial agents with new mode of action is enormous. In the strive for new antibacterial agents that inhibit pilus assembly, an important virulence factor, routes to introduce triazoles in position 8 and 2 of ring-fused bicyclic 2-pyridones have been developed. This was made via Sonogashira couplings followed by Huisgen 1,3-dipolar cycloadditions. The method development made it possible to introduce a diverse series of substituted triazoles and their antibacterial properties were tested in a whole cell pili-dependent biofilm assay. Most of the twenty four candidates tested showed low to no activity but interestingly three compounds, one 8-substituted and two 2-substituted, showed promising activities with EC50's between 9 and 50 μM.

Design and synthesis of peptides from bacterial ParE toxin as inhibitors of topoisomerases

Toxin–antitoxin (TA) proteic systems encode a toxin and an antitoxin that regulate the growth and death of bacterial cells under various stress conditions. The ParE protein is a toxin that inhibits DNA gyrase activity and thereby blocks DNA replication. Based on the Escherichia coli ParE structure, a series of linear peptides were designed and synthesized by solid-phase methodology. The ability of the peptides to inhibit the activity of bacterial topoisomerases was investigated. Four peptides (ParELC3, ParELC8, ParELC10 and ParELC12), showed complete inhibition of DNA gyrase supercoiling activity with an IC100 between 20 and 40 μmol L−1. In contrast to wild-type ParE, the peptide analogues were able to inhibit the DNA relaxation of topoisomerase IV, another type IIA bacterial topoisomerase, with lower IC100 values. Interestingly only ParELC12 displayed inhibition of the relaxation activity of human topoisomerase II. Our findings reveal new inhibitors of bacterial topoisomerases and are a good starting point for the development of a new class of antibacterial agents that targets the DNA topoisomerases.

Identification of a Novel Protein Synthesis Inhibitor Active against Gram‐Positive Bacteria

In an effort to identify novel antibacterial chemotypes, we performed a whole-cell screen for inhibitors of Staphylococcus aureus growth and pursued those compounds with previously uncharacterized antibacterial activity. This process resulted in the identification of a benzothiazolium salt, ABTZ-1, that displayed potent antibacterial activity against Gram-positive pathogens. Several clinically desirable qualities were demonstrated for ABTZ-1 including potent activity against multidrug-resistant clinical isolates of methicillin-resistant S. aureus (MRSA) and vancomycin-resistant enterococci (VRE), retention of this activity in human serum, and low hemolytic activity. The antibacterial activity of ABTZ-1 was attributed to its inhibition of bacterial translation, as this compound prevented the incorporation of [³⁵S]methionine into S. aureus proteins, and ABTZ-1-resistant strains were cross-resistant to known inhibitors of bacterial translation. ABTZ-1 represents a promising new class of antibacterial agents.

Modulation of antibiotic resistance in bacterial pathogens by oleanolic acid and ursolic acid

Antibiotic resistance among bacterial pathogens is a serious problem for human and veterinary medicine, which necessitates the development of novel therapeutics and antimicrobial strategies. Some plant-derived compounds, e.g. pentacyclic triterpenoids such as oleanolic acid (OA) and ursolic acid (UA), have potential as a new class of antibacterial agents as they are active against many bacterial species, both Gram-positive and Gram-negative, and specifically target the cell envelope. The aim of the present study was to investigate the influence of OA and UA on the susceptibility of four bacterial pathogens (Pseudomonas aeruginosa, Listeria monocytogenes, Staphylococcus aureus and Staphylococcus epidermidis) to the β-lactam antibiotics ampicillin (Ap) and oxacillin (Ox). Antimicrobial assays were conducted with bacteria growing in liquid suspension cultures (planktonic cells) or as biofilms. Using FICI value estimation and the time–kill method it was demonstrated that in some combinations, the tested compounds acted in synergy to lower the susceptibility of S. aureus, S. epidermidis and L. monocytogenes to ampicillin and oxacillin, but no synergy was observed for P. aeruginosa. These results indicate that OA and UA may be useful when administered in combination with β-lactam antibiotics to combat bacterial infections caused by some Gram-positive pathogens.

Small organometallic compounds as antibacterial agents

The emergence of bacterial resistance to commercial antibiotics is an issue of global importance. During the last two decades, the number of antibacterial agents that have been discovered and introduced into the market has steadily declined and failed to meet the challenges posed by rapidly increasing resistance of the pathogens against common antibacterial drugs. The development of new classes of compounds to control the virulence of the pathogens is therefore urgently required. This perspective describes the historical development in brief and recent advances on the preparation of small organometallic compounds as new classes of antibacterial agents with potential for clinical development.

Pleuromutilin and its Derivatives-The Lead Compounds for Novel Antibiotics

Due to the rapid onset of resistance to most antibacterial drugs, research efforts are focusing on new classes of antibacterials with different mechanisms of action from clinically used antibacterials. Pleuromutilin derivatives have received more and more scientific attention for their unique mechanism of action. Two pleuromutilin derivatives, tiamulin and valnemulin have been successfully developed as antibiotics for veterinary use. Retapamulin, another pleuromutilin derivative has been approved for use in humans in April 2007 by Food and Drug Administration (FDA). It has been shown that there is rarely cross-resistance between pleuromutilin derivatives and other antimicrobial agents, and the development of resistance bacterial is still low. This review will demonstrate mechanism of action of pleuromutilin derivatives and reveal the structure-activity relationship (SAR) of pleuromutilin derivatives. Additionally, the pleuromutilin antibacterial derivative agents in the market, such as tiamulin, valnemulin and retapamulin, will be discussed. It is proposed that new antibacterial agents might be developed from pleuromutilin derivatives in the future.

Newer antibacterials in therapy and clinical trial

In order to deal with the rising problem of antibiotic resistance, newer antibacterials are being discovered and added to existing pool. Since the year 2000, however, only four new classes of antibacterials have been discovered. These include the oxazolidinones, glycolipopeptides, glycolipodepepsipeptide and pleuromutilins. Newer drugs were added to existing classes of antibiotics, such as streptogramins, quinolones, beta-lactam antibiotics, and macrolide-, tetracycline- and trimethoprim-related drugs. Most of the antibacterials are directed against resistant S. aureus infections, with very few against resistant gram-negative infections. The following article reviews the antibacterials approved by the FDA after the year 2000 as well as some of those in clinical trials. Data was obtained through a literature search via Pubmed and google as well as a detailed search of our library database.

Pyrrolamide DNA gyrase inhibitors: Optimization of antibacterial activity and efficacy

The pyrrolamides are a new class of antibacterial agents targeting DNA gyrase, an essential enzyme across bacterial species and inhibition results in the disruption of DNA synthesis and subsequently, cell death. The optimization of biochemical activity and other drug-like properties through substitutions to the pyrrole, piperidine, and heterocycle portions of the molecule resulted in pyrrolamides with improved cellular activity and in vivo efficacy.

In Vitro and In Vivo Activities of Novel, Semisynthetic Thiopeptide Inhibitors of Bacterial Elongation Factor Tu

Recently, we identified aminothiazole derivatives of GE2270 A. These novel semisynthetic congeners, like GE2270 A, target the essential bacterial protein elongation factor Tu (EF-Tu). Medicinal chemistry optimization of lead molecules led to the identification of preclinical development candidates 1 and 2. These cycloalklycarboxylic acid derivatives show activity against difficult to treat Gram-positive pathogens and demonstrate increased aqueous solubility compared to GE2270 A. We describe here the in vitro and in vivo activities of compounds 1 and 2 compared to marketed antibiotics. Compounds 1 and 2 were potent against clinical isolates of methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci (MIC(90) ≤ 0.25 μg/ml) but weaker against the streptococci (MIC(90) ≥ 4 μg/ml). Like GE2270 A, the derivatives inhibited bacterial protein synthesis and selected for spontaneous loss of susceptibility via mutations in the tuf gene, encoding EF-Tu. The mutants were not cross-resistant to other antibiotic classes. In a mouse systemic infection model, compounds 1 and 2 protected mice from lethal S. aureus infections with 50% effective doses (ED(50)) of 5.2 and 4.3 mg/kg, respectively. Similarly, compounds 1 and 2 protected mice from lethal systemic E. faecalis infections with ED(50) of 0.56 and 0.23 mg/kg, respectively. In summary, compounds 1 and 2 are active in vitro and in vivo activity against difficult-to-treat Gram-positive bacterial infections and represent a promising new class of antibacterials for use in human therapy.